Fuel tank installations at service stations having underground tanks, have long had the problem of water entering from the manhole structure above a tank and draining downwardly into a sump structure above a tank. The problem is particularly acute where high ground water levels of underground water tables extend to within a few inches of the ground surface.
In the prior art, sump covers have generally been utilized to prevent such water from entering the sumps, as by draining down via the manhole cover, etc., into the sump. Such sump covers are generally effective for a while after installation. However, when it is necessary to remove such cover, as for inspections, etc., workers often do not re-secure the cover correctly. Threaded fasteners have long been utilized in the installation of sump covers. In the tightening of such threaded fasteners, both in initial installation and in later closures after openings, as for periodic inspections required by law, leakage can occur. As a result of human error, uneven tightening of the threaded fasteners or screws can readily occur, as when tightening a cover or structure with a gasket or O-ring, with one screw being tightened too tightly relative to other screws, resulting in tilting of a cover with resultant leakage. Disassembly may occur, or a screw may be omitted, or a screw not tightened at all.
The present invention provides positive sealing with application of only relatively limited pressure. Positive sealing is provided at the level of the sump and higher in a manhole to prevent leakage, even when totally submerged, thus to prevent contamination of ground soil.
The present invention eliminates the sump cover of the prior art, and the problems associated therewith, and provides a bladder seal which prevents entry of water from above, as via the manhole cover or other leakage into the sump, typically caused by high ground water level leakage. The manhole cover and its annular resilient seal normally prevent such entry.
Improved positive sealing according to the invention is provided by a manhole skirt communicating with the interior of a sump, and a bladder seal having spaced-apart first and second portions, and a bladder portion therebetween the first portions being secured in sealing engagement with an upper surface of the sump, and the second portion of the bladder seal being sealingly engaged by being compressed about an inner surface of the manhole wall. The first bladder seal portion is preferably secured by clamped engagement with a flange portion disposed about a sump opening communicating with the manhole skirt, and the second bladder seal portion is preferably sealingly engaged with the manhole wall by an expansion ring with segments urged apart by expansion bolt mechanisms.
An observation port opening in the manhole cover is closable by a lid member which is opened and closed by operation of a latch mechanism. With the observation port open, the sump interior is readily viewed to ascertain whether or not water has entered thereinto from above. The observation port eliminates any necessity for the opening and lifting of a heavy manhole cover, normally requiring two persons, then reaching down and removing a sump cover by removing threaded fasteners, etc., in order to determine whether there is water in the sump.